1. Field of the Invention
The present invention relates to the field of accessories for radiotelephones.
It relates more particularly to using radiotelephones in a car, which imposes particular human factors difficulties, given the manifest safety constraints when such an appliance is used in a moving vehicle.
2. Discussion of Prior Art
A particular object of the invention is to enable automatic number-dialing means for the radiotelephone to be used under voice control in a vehicle.
The radiotelephones available on the market all have systems constituting a directory and telephone dialer, is however those systems require keys to be pressed, menus to be scrolled on the screen of the display, etc., thereby making them difficult to use in practice in a vehicle.
EP-A-0 650 283 describes a self-contained portable appliance forming a directory and telephone dialer and including in particular voice recognition means suitable for analyzing a name spoken into a microphone, for addressing a call number memory to find the number associated with the correspondent whose name has been spoken, and then producing a sequence of voice frequency tones (DTMF signals) corresponding to the various digits of the number found in that way.
U.S.Pat. No. 4,737,976 teaches apparatus of that type integrated in a car radiotelephone, in particular to enable it to be used in a "hands-free" mode of operation, without it being necessary to take hold of the handset to dial the number.
When it is desired to proceed in that way, a first difficulty is the high level of noise in a vehicle cabin. In particular, if it is desired to use the appliance in "hands-free" mode without detaching it from its support, the large distance between the microphone and the user gives rise to a relatively high level of noise which makes it difficult to extract a useful signal buried in the noise.
For that purpose, above-mentioned U.S. Pat. No. 4,737,976 proposes providing a dynamic noise suppressor stage operating by spectral subtraction upstream from the voice recognition proper. In practice, that apparatus presents only limited performance when it is desired to achieve fine recognition (e.g. in a file of voice signatures containing several tens of references, or even more than a hundred references) and to do so in very noisy surroundings, typical of the environment of a car, with spectral characteristics that are not stationary, i.e. which vary in unpredictable manner as a function of driving conditions (driving over bumpy roads or on paving stones, car radio in operation, etc.).
Another difficulty, still when it is desired to use the appliance without detaching it from its support, stems from the fact that the appliance must be very ergonomic to use since it will generally be too far away for the user to be able to read the messages on the display of the radiotelephone or to press on such and such a key of its keypad, or at least the user will not be able to do so in a manner that is not dangerous for driving, if the vehicle is moving.
These two major constraints (high noise level and the search for excellent human factors) have not succeeded up to the present in enabling a radiotelephone to be used in a completely "hands-free" configuration in a vehicle in a manner that is satisfactory for the user and for driving safely.